As an example of a membrane filtration apparatus for filtrating a raw liquid through a membrane element to produce a permeated liquid, known is a membrane filtration apparatus equipped with a membrane element having a membrane wound body formed by winding a membrane member, and with a pressure-resistant vessel in which this membrane element is accommodated.
A membrane wound body in the membrane filtration apparatus of this type is formed by winding a membrane member up. Thus, the membrane member may be shifted out of position into the axial line direction by pressure in the axial line direction that is received from, for example, a raw liquid flowing the pressure resistant vessel, so that the membrane wound body may be deformed into a telescope form. Against such a problem, a technique is known in which an end member (so-called telescope preventing member) is fitted to an end surface of the membrane wound body to face an end surface of the body, thereby preventing the membrane member from being shifted into the axial line direction (Patent Document 1 listed below).
An exterior member is laid onto the outer periphery of the membrane element. This exterior member is fitted thereto so as to stride across the outer periphery of the membrane wound body, and a portion of the telescope preventing member. As described in Patent Document 2, in this case, the exterior member is generally formed by winding a glass fiber to which an adhesive is applied (glass fiber roving) onto the outer periphery of the membrane wound body.
Also, as described in Patent Document 1, conventionally, the following types exist as the telescope preventing member: a type of having, at a portion of the member to which the membrane wound body is butted, a cylindrical moiety (skirt) into which the membrane wound body is fitted; and a type of not having such a cylindrical moiety.
However, according to the former type, it is necessary to control the outside diameter of the membrane wound body at a high precision to be matched with the inside diameter of the cylindrical moiety. Moreover, the outside diameter of the membrane wound body is restricted so that a limitation is imposed onto an increase of the membrane in area. Thus, the latter type, which has no cylindrical moiety, is becoming the mainstream. However, the latter type has a problem that at the time of the winding the glass fiber roving, the glass fiber roving is depressed down at the boundary between the membrane wound body and the end member.
For this reason, Patent Document 3 suggests a telescope preventing member in which, at its portion to be butted to an end member, plural protrusions are circularly located to prevent the glass fiber roving from being depressed down.